Somebody who is more familiar with Canadian business law would know for sure, but I think that it is because technically, foreign businesses (and that includes American ones) are not allowed to operate directly in Canada.
Of course, one sees evidence to the contrary all the time–Canada has Wal-Marts, Ford and GM and Chrysler factories, Xerox machines, Coca-Cola, and many McDonald’s and Starbucks, among other US-based companies.
But really, the companies with the maple leaf in their logo are Canadian. They have been incorporated under Canadian law as Ford of Canada, or McDonald’s of Canada, or IBM of Canada. The foreign parent generally owns all the shares of the Canadian company (thereby raking in all the profits), but the Canadian head office does the planning and runs the daily affairs of the Canadian branches or outlets or factories or whatever.
Since they are technically Canadian companies, they show it by using a maple leaf or some other identifiable Canadian icon somewhere in the logo.
I apologize for having no cites for this, but this attempt at answering the OP comes out of my experience. Some years ago, I was working for the Canadian branch office of a small US-based firm. The head office in Tampa, Florida decided it didn’t want to set the Canadian branch up as a Canadian company, and went ahead and operated the Canadian branch as if it were in the US–they transplanted American managers (who reported directly to Tampa) to the office in Toronto.
They did keep a small bank account locally for payroll and other expenses, so my paycheques were in Canadian dollars although they showed my zip code (!) and SSN (!). There were other oddities associated with the setup, but I won’t go into them here.
Anyway, this did not go over well with the Canadian authorities, who, IIRC, basically told the company that it had to incorporate under Canadian law if it wanted to run a Canadian operation. It also had to employ Canadians as officers of the resulting Canadian company. The upshot was that head office in Tampa decided that complying with Canadian law was too much of a hassle, so they closed the Toronto office, packed up, and went home.
Oh, and they laid us all off too. Thank you very much, Tampa.
Anyway, that’s my answer. But if anybody knows (and can cite) Canadian business law, I’ll defer to their answer.