Let's be factual. Western provinces and Quebec are not under-represented in the House of Commons, as proportional representation applies. However, there is under-representation in the Senate, and that is a real problem and a real challenge, but it has unfortunately become a constitutional taboo.
In the House of Commons, the principle of proportional representation is the result of a historic compromise negotiated in 1867. Through the Act of Union, to propagate an assimilation policy of French Canadians, Lord Durham recommended a principle of equal representation, which made it possible to under-represent francophones' political weight at the time. Francophones from Quebec in particular and from Canada in general were under-represented from 1840 until the demographic shift of 1850, and that was a great historic injustice. That is why, in 1867, they rallied to the idea that proportional representation contained a certain ideal of justice in the distribution of seats, but that, on the other hand, it should be part of a nation-to-nation pact.
However, Quebec never could have anticipated that the result of that Confederation would be Regulation 17 or a disregard for Manitoba's language rights. It was naive in its belief that the development of the Canadian west would perpetuate the political weight of francophones and anglophones, as was the case in that small Canada with four partners created in 1867.
The results did not make it possible to implement the pact made in 1867 and the related promises. As a result, the relationship between Quebec and Canada is now on the decline. Is that decline Quebec's or Canada's fault? That is a political debate I will not engage in. How to improve the situation? It is not simple.