I filled in the postal code.
In the Canadian form the weights and measures are in kg and cm, since we are metric.
I have filled in those blanks and the pop-up says
'invalid pounds' and invalid measurements.
So I'll try in pounds.
This is, of course, using calculated shipping as under Canada Post we cannot ship for a flat rate and it costs more to ship to New Jersey than California.
I may try filling in with the Canada Post parcel sizes, but that adds a huge amount to my cost of shipping.