goldminer, There is not one answer to your question, there are variables.
First, you have to realize that the Oneida Community factories in New York and their factory in Niagara Falls, Ontario, Canada were only about 200 miles apart. The Canadian factory was mostly for the purpose of avoiding import/export taxes and fees when selling traps across the border. A lot of the parts, especially cast parts like Bear and Wolf trap pans with embossed, raised letters, were all made in the Oneida Community foundry in New York and transported to the Ontario factory. Smaller cast trap pans were blank and could be stamped at the Canadian factory. Most of the production at the factories was of trap parts that were assembled in a different part of or in a totally different facility.
So, you have to separate the small traps and the bear traps as the pans on all Newhouse Bear and Wolf traps, U.S. and Canadian have the N.Y. address on them. The smaller traps will generally not have the "N.Y." on the pan if it is a Canadian trap. On the smaller traps, the pan lettering on Canadian traps is usually larger and will lack the N.Y. Some of the older, smaller, Newhouse, New York made traps do have a somewhat larger number in the center of the pan but also have the N.Y., that does not make them Canadian.
Spring stamping is variable, early Canadian stamps lack the N.Y., latter ones will have "ONT." and the last ones will have "made in Canada". Just because you cant see the N.Y. on a spring stamp does not make it a Canadian trap, many stamps are not completely legible so the N.Y. may have been there you just can't see it. Also, some Canadian Newhouse traps will have unstamped springs like a Hawley & Norton. There is an arched "S. Newhouse, Oneida Community" spring stamp, this is the Canadian version of the arched "Kenwood, N.Y." stamp. A lot of spring stamps are not legible for any number of reasons, but if you cant tell if it is a Canadian trap or not, then it really does not mater. Canadian traps are more desirable because they are different and less common. So, if it doesn't jump out at you, then it is just another Newhouse trap, not all of them are collector traps.
A few Canadian smaller traps will have "made in Canada" stamped on the base, dog or underside of the pan.
Canadian Newhouse trap pans
Canadian Newhouse trap spring stamps