The MDA/DA and visibility minimums called for on the approach plates apply to all civil airplanes except where regulations or operations/management specifications define different minima to be used. (such as might be the case with part 135 or 121 operators)
For operations conducted under part 135, the reported weather conditions must be at or above published mins in order to begin the approach. If an updated report is recieved after commencing the final approach segment which indicates below minimum conditions now exist, the approach may be continued. If upon reaching the MAP or DA, the PIC determines that the required
flight visibility exists, then descent below MDA/DA and a landing may be accomplished.
When operating under part 91, you may execute the approach regardless of the reported weather. The PIC must still determine that the required
flight visibility exists in order to descend below MDA/DA and land. So in your case it appears that the prohibition against beginning the approach when conditions are reported below minimums does not apply unless Canadian regs are more restrictive. The full text of 91.175 available HERE
http://ecfr.gpoaccess.gov/cgi/t/text...2.6.39&idno=14
Hope this helps.
Best regards,
Westhawk