I got all the answers:
Clinic exposure: every single Canadian school is trash compared to US in clinical exposure amount across the board , and Western is definitely no exception. You may get more exposure to complicated cases (except for ortho) at Western but it overall exposure will be low.
Opportunity after graduation: well if you want to practice in Canada it saves you from writing 2 boards than if you went to a US school, other than that I don't think it matters much which school you went to. With regard to jobs, the connections with sales reps/part time dentists may make it easier to find a job in the surrounding London area, but there are many ways to network outside the school as well. With regard to specialty, all 3 people I know of in my class, that actually applied to specialties in the US got in this year. Same with GPR/AEGD, I only know of 1 reject from a GPR.
Boards: pretty much zero instruction, you study for the boards on your own and that's probably true everywhere, we pass along resources as a class amongst each other. However I have seen some good review courses/resources come out of US schools, but you'd do best to ask the specific school.
Workload: It's a bit uneven across the years, and at least 50% of your clinical years is wasted on stupid admin and misc matters. Support is good from your peers, we have great notes and generally try to help the lower years do better than we did. From faculty it is uneven once again, but by and large everyone wants you to graduate.
General comment: I personally think clinical education is just so much better in the US as a whole, however within 1 year of practice you'll catch up, and your debt load is about 40-50% less if you go to a Canadian school. You get what you pay for essentially, and the final decision is yours.
Feel free to PM me for any more specific questions.