You can contact professors, but don't need to at all in the US and, I think, Canada. An advisor is chosen later, not at the very start of study. The early study is mostly advanced coursework leading to the qualifying exams. One can delay choosing a specific area and an advisor for quite a while.
You might have an "advisor" assigned to help you choose courses and navigate the specific system, but they need not be your research advisor.
Also, some professors, knowing the above, won't respond to emails until you get accepted. Those that do respond are most likely to just encourage you to apply in the normal manner. They will have little impact on the process. You might be just as well off, getting into the program and then going to visit a few professors in person. Especially those teaching your courses. This lets you evaluate whether there is both a personal and a research compatibility.
In particular, I don't recommend flooding them with information about yourself. They aren't part of the admission process most places unless they are on the admissions committee itself. And in that case they need to take a neutral approach since they are responsible for evaluations.
In other places, and in some fields, this won't be the same. In some lab sciences, especially in Europe, the PI actually hires (grant money) people as part of the admissions process. This is rare in the US. Canada seems to be similar as far as I can tell.