There are a few issues that you may want to consider. In some provinces, in order to get a license, you need more than the LMCC's. You may also need certification from either the Royal College of Physicians and Surgeons or the Canadian College of Family Physicians. I believe that Alberta requires that you need both the LMCC's and College certification. The best time to write teh LMCC's is when the material is most relelvant. Part I would best be taken when you are finishing med school. The more that I look at it, it seems a bit harder than the Step 2. In one section of the exam, we have to pick from a list of admission orders and we are docked marks for incorrect and excessive orders. (And some questions are like: Should you get 'lytes at q2h, q1h, or q4h?). The best time to write part 2 of the LMCC's is 18 months into residency because it's an OSCE on general family medicine concepts (and if you're in a field other than family medicine, you're more likely to remember your general clinical skills when you're closer to med school).
Regarding where to do residency: I think that it would be more helpful to do your residency in Canada if you want to practice there. It may be more difficult to get College certification coming from a residency in the US, simply because some programs in the US may not meet the standards set by the Colleges (and because most Canadian residencies groom their graduates for the College exams). Because of this, you may not qualify to sit for the College exams (eg. The Canadian College of Family Physicians requires that Family Medicine residencies have four month block rotations of family medicine). For this reason, it may be easier to do your residency in Canada.
If you are looking to go into family medicine, right now there are many residency positions available. If you are looking into peds or internal medicine, you have to remember that these are consultant residencies in Canada and are not primary care. Additionally, after this years match, there was only one position open in internal medicine and no pediatric positions (one peds neuro though). Additionally, as a DO, you are an unknown commodity. There are only a handful of practicing DO's in Canada and most program directors do not know what a DO is. You would be fighting an uphill battle to get into a residency or job.