Canada is a country of regions, federally united by the British North America Act, 1867 ( now referred as the Canada Act after patriation in 1982). It is also a bilingual and multicultural society with two major (at founding) religion and many others like Hinduism, Sikhism and Islamic etc. 
   The Cabinet which is the center of power is "  federalised". This means that many factors such as regions/ provinces, language, religion, ethnicity, gender etc. must be taken into consideration when the Cabinet is chosen.
     Each province must be represented; the large provinces like Ontario, Quebec must have more members; language, English and French are key and so is religion... Catholic ( Quebec) and Protestant ( Ontario and others), regions with distinct and very important agriculture and industry must be represented and the growing multicultural population has become a top priority too.
     So here we go......1. Each province. If no one is elected from the governing party, then a Senator from that prov. may be selected or someone else from another party ( like when Horner, a Conservative joined the elder Trudeau's cabinet),.or someone, not elected but who  must then seek election. 
                                2. Large provinces like Ontario (4-9) and Quebec (4-7) and B C  (2-4)
                             . 3.  there must be at least one English speaker from Quebec and at least one French speaker from outside ( maybe New Brunswick, the only official bilingual province)
                              4.Protestant, Catholic representation, usually Quebec/Catholic and OPntario etc. Protestant.
                              5. Finance usually go to Toronto; Agriculture to the Prairies or S. Ontario; Justice to Quebec ( Civil law); Fisheries to Maritimes or B C ; Forestry to B C or Quebec; Ethnics ( usually Jewish, Italian, Greek, Sikhs when Liberals are in power and Ukrainian, ( especially) when Conservatives are in power, also the already mentioned). 
                          6. Maybe younger members may be appointed as Junior ministers to allow them to get some experience and also to try to attract young voters 
     In the just concluded election, the Liberals will form a minority government and they did not elect anyone from the resource and agriculture rich, Saskatchewan or Alberta and must find someone to represent these two provinces in the Cabinet. Perhaps Trudeau ca appoint, long-serving  Ralph  Goodale ( who lost his seat) to the Senate and name him to represent Sask. and must find someone from Alberta ( probably do as his father did and lure a Conservative
     It is a time-consuming and very delicate task and it is perilous to ignore the " cabinet conventions".

     The election is over but the " spin" takes over. 
Trudeau claims a " clear mandate", Scheer's Conservatives won the popular vote; the Bloc is revived and the NDP finds itself broke.
What is " clear mandate"? If he is saying that he will govern with respect and responsibility; that he will heed the call for transparency; that he will not coddle rich donors and corporations; that he understands the message fro Sask. and Alberta, where the Liberal won no seats; that Committees will be more amenable to Opposition concerns O( he has to, because now Committees will not be dominated with a Liberal majority and that he will not , like Joe Clarke in 1979 govern as if " he has a majority", but more like his father in 1972, getting the support of the NDP and Greens and even the Bloc.
    The lost 29 seats, including that of " old war horse" Goodale; the Conservatives won the popular vote and increased by 26 seats; thw NDP lost 15 seats the Bloc picked 22 and the Greens i.
     The seat count is ...Libs. 157; the Cons. 121; the Bloc 32; the NDP 24; the Greens 3 and the PC of Bernier none. Former Lib.Justice minister Wilson-Raybould won as an Independent but Philpott lost.
The 33.06% that the Liberals won is the lowest since 1867 ( Canadian Union), when John A. MacDonald formed a government with 34.8% of the votes. This is not a " clear mandate"
for Trudeau

Thisd election once again exposes the flaws of the " 1st past the post:, which favors a two party system.
If this election had been under Proportional Representation, The Conservatives would have won 117 seats, the Liberals 112; the NDP, 54; the Bloc 26; the Greens 22 and the PPC 5; Ind. 1....
     In 1979, Pierre Trudeau's Liberal won more votes but the Clarke Conservatives won more seats.
     Justin Trudeau can govern     for the next two years at least. He will need support from the NDP and the Greens for a progressive program on such issues as climate change, pharmacare etc. and on pipelines, the Conservatives will grudgingly support him.
This government can last, because the NDP is broke and cannot fight an early election and the Bloc will want to savor its " come back".,The Conservatives, well , they may soon have a leadership battle ( they just love to "eat" their leaders).
Minority governments have been good for Canadians ( Pearson from 1963-1968 and Trudeau sr. 1972-1974 are great examples. This type of government will have to make compromises, take the concerns of the other parties, especially the NDP and  even the Bloc, but here it has to be careful,not to be drawn into its nationalists demands and it has reckon with " western alienation" ( Pierre Trudeau lost the West because of his arrogance..." I was not elected to sell your wheat",Petro Canada but Chretien won some back with his reconciliation politics). Trudeau can learn from these examples... less Trudeau and more Chretien.
    Now let  the"ball" roll.