Here's the issue. You get snagged at the US border (port of entry, airport, port, etc...) and just admit that at some point you smoked this weed. What info is shared Nation to Nation? Does a US Border Guard have access to Canada's CPIC to check your criminal record? If the US places you on a 'No-Fly" list, how many other countries have access to that US list? If you get black-balled for the US, what other countries will have access to that same black-balling to also treat you in the same way based on an American decision? I think this is the door that has been opened and with the expanded shared information agency to agency and nation to nation since 9/11 people are going to get absolutely screwed over in totally unexpected ways.