You are not regarded as an IMG (all Canadian medical schools are members of the LCME) -- you enter the first round of the US match with other US students. You will have to withdraw from one match if you match with the other (I forget which comes back first).
In terms of visas, the easiest and most common is a J-1 visa (educational). The problem with this is you have to come back to Canada for 2 yrs after residency. The more versatile visa is the H1B which will allow you to stay in the US +/- get a green card without returing to Canada.
The H1-B requires much more leg-work and lawyering -- generally only middle/lower tier schools will support this. The top schools generally do Js only.
If your goal is to practice in the US, you may also consider doing your residency in Canada and moving to the US afterwards (most Canadian Residencies make you American Board-eligible -- check the relevant specialty board websites), when it is generally easier to get the needed visas.
I should add that practicing in Canada after completing an American residency is often difficult and may require additional residency training (some Cdn programs are longer). You may want to talk directly to the Royal College if this is your plan.
