First my quick answers.
1 .Going though these forums it seems that it's easier to get a Masters degree at a top school because they are generally considered 'cash cows' for the school. True?
2. Is it possible to get a Masters degree at a top US university without doing research?
3. If I explained that I wanted to do a project on forwarding physics education would this help my chances?
Really depends on the program. If it is a physics department known for physics education or they have people who specifically mentioned in their research interests physics education, then it could help. However, if no one in the department mentions anything about physics education, then it probably hurts you since that is not the departments focus. But you probably shouldn't be applying to that program anyways.
Before you say, "Highschool teachers don't need a Master's degree," in Canada you are paid more if you have a masters and if I could go to a top school, why not?
I can provide one why not. However, it is most directly relevant to Wisconsin, and I think applies to the US in general. Not sure about our northern neighbors, but I have a feeling it is relevant since it is about pay.
I was a school board member and I know that some people are hesitant to hire people straight out of school that have a masters. Remember, you are more expensive, so that is strike one. Strike two is that your masters is not in education. And your third strike is a combination of one and two: you are more expensive and don't have actual teaching experience. When they pay other teachers more for their masters, they have already been working so they know what they are getting for you money.