Some schools will give weighting to your degree results, but for others, after you satisfy entry requirements (which are usually 2.1 or higher, sometimes 2.2), they do not matter in the selection process.
You will probably need to contact individual schools to find out what classification your degree is equivalent to (but first just try googling - I am sure there is some sort of conversion between Canadian and UK degree results). A lot of schools are very responsive, although right now they might be too busy with this year's admissions. Also, most schools have "International" sections on their applicant websites, where they explain what satisfied their entry requirements and what does not. If you can't find this for Grad Med - try looking at some Master's programmes admissions webpages, they might have more info about degree conversions.
Some form of admissions tests (UKCAT, GAMSAT, BMAT) is required for the vast majority of GEM programmes, with some exceptions (Cambridge, Birmingham come to mind) - just do your research about each school's entry requirements, there aren't that many GEM programmes in the UK, relatively speaking.