IIRC, there were a couple of different tiers to Canadian grad schools where one group required a slightly higher GPA than the other. McGill would probably be one of those with the higher standard which was around a B+ or 78 out of 100 which I'm not sure if a 3.5 is quite that high so it may be borderline. There were other schools that were down a peg and had just a B or 73 out of 100 which I think you would pass, but I last looked at this a few years back. University of Waterloo would be an above average school while the University of Western Ontario would likely be a second tier school, or at least that is what I remember.

Regarding JB King, in the US B+ = 3.5, A = 4.0, B = 3.0, C = 2.0, etc.. You said you are not from Canada, so if the degree is from a US university a 3.5 is a B+. So it might work for Canadian schools that require a B+, it's worth a try.

For top tier schools in the US, the most important thing seems to be the letters of recommendation from other college professors. And that you are capable of doing research. If you have not researched with a college professor many of the top tier schools in the US will turn you down. And if it is a professor that they never heard of, it will be harder. Sometimes you can muscle your way in by taking classes without a major and then meeting the faculty/doing research with them. But it may be different in Canada.

Anyway good luck :)