From my understanding, you need a negative COVID test (I think only a certain kind is accepted) within 72 hours prior to crossing, upload and apply on the Arrive CAN app, and subject to random on site testing when you cross. The biggest hurdle is getting into Canada. Once you get in, getting home is fairly easy. You are a US Citizen, they can not deny your return. If you have parts, depends on where they are made and value if duty is collected. There is no tax on those items, just duty. Tax is more for alcohol and tobacco products. Best to call each port you will be crossing on the US and Canadian side to ask details.