I don’t think the initial two senators would be appointed (when AK and HI became states, they had Senate elections prior to the effective date of admission so that they would have two elected senators from the get-go), but if they were appointed, Gov. Fortuño, who is a Republican, would either appoint two Republicans or, in the spirit of bipartisanship, a Republican and a Democrat.
They are likely to hold the vote as soon as possible and use the “Tennessee Option” to send a delegation to demand seating. I suspect they have the candidates already planned out.