"In BC you are legal if you are legal at home"
is overstatements. When some vehicle requirements can be grandfathered from your home jurisdiction, some will not.
Typical sample are semitrailers, who can be double towed in Canada, WA, OR, but the 2nd trailer needs to be unhooked when entering CA.
Typical RV sample is big motorhome pulling long trailer.
Lot of states allow for the combo to be 75' long, but only 65' in California.
True is that nobody have seen CHP with tape measure in his hand, but the law is there.
Same with DOT scales were never been enforced in the past, but in last years we hear more and more about by passers chasing.