Gunshots in Ixtapa

If the main problem in Mexico is US policy then Canada should be awash in drug cartels, violence, extortion and lawlessness.

Simplistic thinking.
1. Poverty is a root cause of most of these problems. Mexico is mostly a third-world country, awash in poverty. Canada is a first-world affluent country.
2. Mexico's climate is ideal for growing coca, the cartel drug of choice. Canada's climate is not.
3. Canada has first-world law-enforcement and judicial systems. Mexico does not.
4. Canadian farmers can make a good living growing legal crops. Many Mexican farmers cannot.

I'm sure there are many other reasons. Canada is not awash in these problems for the same reasons most other first-world countries are not. Mexico's problems, on the other hand, are similar to those of many other third-world countries. Can you not see the difference?