Multiple Shipping Zones for USPS Module

[thevintagesound]

In my store I have items that vary from a few onces all the way up to 70lbs. I have been using UPS to handle all of my shipping for the US ONLY and USPS to handle shipping for Canada. I've also put in a catch that if someone from outside the US wants to see shipping costs that instead of the "Cannot calculate shipping cost" that it asks them to email me so that I can manually calculate the pricing.

Now with that said. There are some people that want to order a bunch of little parts, with a total weight of 1 lb or so. UPS is charging something like $9-12 to ship them. I'd like to add USPS to be able to ship in the US (as well as Canada) but only for orders with a total weight of 3 lbs or less.

Can this be done?

[thevintagesound]

Anyone?
Basically I want US Mail for Canada for all parts and US Mail for orders that are less than say 5 lbs.