First off congrats on matching!
I don't know what things are like in Canada. Are you planning to stay in Canada or did you mean you were thinking of coming to the US for fellowship? I don't know how things are after you graduate in Canada, so I'm afraid I can't help you much there. But as far as the US is concerned, I or I'm sure many others can try to help.
It's hard to say without knowing a bit more about you what subspecialty to recommend to you. Contrary to some advice you'll hear in various places including from other physicians (some physicians like to rubbish other specialties for whatever reason), I think all subspecialties can be good choices depending on what you are like and what you like. All have their pros/cons. And I'd say don't rule out rheum quite yet - it can actually be quite interesting and good, depending on what you're looking for. But speaking in general terms since i'ts hard to be specific with you:
1. Don't just look at the cool zebras in a subspecialty. Look at the bread and butter pathologies you'll be dealing with day in and day out. For e.g. endocrinology has some interesting pathologies, but you'll most likely be dealing a lot with diabetes, so are you interested in diabetes?
2. Wha'ts the patient population like? Are you interested in dealing with the sorts of people in the subspecialty you're considering (e.g. heme/onc dealing with generally more elderly people with cancer; ID deals with a lot of HIV/AIDS patients), etc.?
3. Do you like a more hands-on specialty, or do you prefer less hands-on specialties? I mean working with your hands. Or somewhere in the middle? Critical care is very much hands-on, lots of procedures, etc. Whereas hem/onc closer ot the less working with your hands side of things.
4. What are the other physicians like? Do you get along with the "culture" of the subspecialty? The (broadly speaking) sorts of personalities who tend to be in a particular subspecialty? Do you feel at home with them? (This is quite variable though but I'm just speaking in broad terms.)
5. If it's important to you, what's the lifestyle like beyond residency/fellowship? What are the hours like? Do they mesh with your goals in life (e.g. getting married if you're single, raising a family if you have kids, living in a certain locale if you need to end up somewhere)?
6. Consider the business side of medicine. What are the available practice environments post-fellowship (e.g. private practice, academics). Where do you want to end up working? Living? Is it difficult to find jobs around where you want to live in your subspecialty?
I'm sure there's much more to say, but I hope these will get you started. Good luck!
