Just posting to concur that the issue really is a matter of the extent to which being a commuter to employment in the U.S. results in
Immigration, Refugees, and Citizenship (formerly "CIC") more thoroughly and skeptically assesses your case.
There have been some
commuter-cases reported in the published Federal Court decisions. Typically they did not go well for the applicant. But also typically there were obvious reasons for this: applying with a minimal margin (making it easy for CIC to question enough days to reduce the calculation below the physical presence threshold), indications of other ties to the U.S. and pattern of activity raising questions about the accuracy of the declared presence, other reasons for concern about the applicant's credibility.
Thus, one of the bigger factors which can influence how things go is the extent of your margin over the minimum physical presence requirements. Hopefully you applied with at least a month's margin or more. Note, for example, in a very recent case,
Abdul-Sattar Q Mahdi 2015 FC 1318), the Federal Court justice described
43 days more than the physical presence requirement, as
"only slightly over the minimum requirement for physical presence in Canada," in discussing the import of potential concern about undisclosed absences. (Here again, there were also many other reasons raising concerns, despite the fact that the Citizenship Judge accepted the applicant's explanations and approved him for citizenship, which the Federal Court set aside.)
To say whether you will run into issues regarding proof of your presence in Canada would be guessing, but the risk is probably substantial. If put to proving your presence (the equivalent of what has been the RQ, or "Residency Questionnaire"), the challenge will be to fully document your presence in Canada. The scope, thoroughness, and especially the credibility or reliability of your evidence to document your presence in Canada would, then, be crucial. Which is, again, to essentially concur in the suggestions to retain, organize, maintain, and be able to present such evidence if the need arises.
