"Cheese is my favorite topping."
Translation:Ost er mitt favorittpålegg.
It would be 'yndlingspålegg/yndlingspaalegg', which is also accepted. This is less common than 'favorittpålegg'.
You cannot write "favoritt pålegg" for instance, but it works when it's not used as an adjective:
"Han var en klar favoritt."
"He was a clear favourite."
... to win the race, to get the job, or to some person.
Yes, but it sounds more natural with "Kanin er favorittdyret mitt". When you say "en kanin" it sounds like you mean a particular rabbit, and not rabbits in general