Western woods: At least when it comes to goods, it would seem that the Supremes could easily say that sec. 121 means that if a good can be legally sold in one province or territory, then it can be legally sold in any other province and territory.  What would have been the point of sec. 121 in 1867 if one province, wanting to block inter-provincial trade,  could simply say that a product from another province did not meet its standards and hence couldn't be sold in its territory? 

Professional standards might be more of challenge for the Supremes, but if they have the will, they could also find that if you are licensed in one province or territory, you are, in effect, licensed in all.