We applied for guardianship of my father. Is it up to us to pay the guardian?

No. If the measure of guardianship is entrusted to a member of the family, it is then exercised free of charge.
 

Sometimes, the guardianship judge or the family council, realizing the importance of the property which needs to be managed or the difficulty of exercising the measure, may award compensation to the guardian, but it is the responsibility of the person protected (article 419 of the Civil Code)

If the guardianship measure is exercised by a legal representative, only the protected person participates in the total or partial financing of the professional according to his income.