The 51% "rule" doesn't only says that ONE PERSON has to build 51% of the aircraft, just that "amateur builders" (i.e., not the kit manufacturer) perform 51% of the tasks. But your issue (if I understand you correctly) is you intend to certify as a Canadian Amateur Built aircraft and then possibly sell to a buyer who would like to register it in the US. If that is the case, here is the guidance for getting that registration approved: https://www.faa.gov/documentLibrary/.../AC_20-27G.pdf