UCD gives you about 9 weeks of summer after 3rd year, where you can do electives before submitting ERAS/CaRMS (applications for residency in the states and Canada). I did a month long internal med elective at Western, a month of family medicine at Emory (Atlanta, GA), then I skipped the first week back of UCD to do 2 weeks with a family doctor at her private clinic in London, ON. 10 weeks total for the summer, only one month in the states! January of fourth year is also off at UCD, and did another month long family medicine elective at Mayo Clinic (Rochester, MN). Despite my applications already being in, I was highly interested in that program, so used the month as an "audition" to show them my abilities and enthusiasm and I figured if I didn't match, it would be an extra elective on my CV. Schools generally don't let students come for electives once you are graduated.
I did apply to both CaRMS and ERAS, Canada and the States. Personally, I was couples matching which made CaRMS tricky. In CaRMS, there are set spots for IMG's and set spots for Canadian grads. So for example, if there are 10 spots in Winnipeg for family medicine, 1 MUST be filled by an IMG, and 9 must be filled by Canadian grads. It forces them to take IMG's, but usually only one per program. In ERAS, anyone can apply for any spot, they don't have to take IMG's, or they can choose to take mostly IMG's. Since me and my partner both wanted family med, we didn't apply to any Canadian programs which only took 1 IMG as we didn't want to be apart, unfortunately that's most programs. Second issue was, I unfortunately didn't get the NAC OSCE cut off for Ontario family med, so that limited me as well. I was unwilling to compromise and choose a specialty in Canada with lower NAC OSCE cutoffs. No problem for the states, we got plenty of interviews and matched together into the same fm program. Obviously a personal decision for me to limit my CaRMS options, but its always a good idea for IMG's to have the states as a backup. There are only about 120 FM spots for IMG's in Canada, whereas there are 7000-8000 family med spots IMG's can apply to in the states for FM.
As for Visa things, for Canadians to work in the states, you require a visa. The J1 is the only one you would be eligible for if you're going into residency straight out of med school. This is a "non-immigrant" visa and requires you to leave the country for 2 years after residency, unless you complete a J1 waiver agreement, where you sign a US government contract to work in a rural area. In order to get the J1 visa, Health Canada must give you a statement of need. This is basically saying, since you have to leave the states afterwards, there is a need for your specialty in Canada. Health Canada decides which specialties they give statements of need for, and they put limits on the number they give out. This information is available here:
http://www.hc-sc.gc.ca/hcs-sss/hhr-rhs/postgrad-postdoc/cat_b-list-liste-eng.php. If you want to train in a specialty that's not listed there, you cannot do so in the states as a Canadian. If your specialty is on this list, you just have to apply for the statement of need within the number they give out. The application for the statement of need is simple, it was a 2 page form and I sent it in by email within minutes of getting my match results and was told I was within the limit. I had a friend who did the same with OB, and even though they only give out 20 statements of need for OB, he was in the limit. Getting the statement of need and J1 is really not a worry if your specialty has statements of need available.