Looking for advice on fighting Christians as a Norse pagan

I started a game as Erik the Heathen in the William the Conqueror scenario. After some false starts, I managed actually get established.

I currently control Norway, northern Sweden, and most of Finland. However, the remaining Scandinavian Catholics are still being a real pain in the ass. The HRE is also really scary.

My only CBs against these guys are single-province conquests, which really is not effective. What is the best way to fight them?