Can two GFCI outlet loads be powered by two separate circuits?

It may be possible to add a circuit and split where things are fed from. The best option would be to add heavy duty covers or in use covers with proper seals as code requires on outside receptacles in wet locations this keeps the receptacles dry so they won’t be the cause of the trip. If the garage is attached to the home adding circuits is much easy and less restrictive rules apply than for a detached structure.