Starting canisters, HOB, ect
I start my canister filter with an aquarium vacuum. Just pop the input uptube off the filter and stick the small end of the vacuum tube against it (doesn't have to fit tight). Lower the whole vacuum under the water level until it's full of water, then lift the wide end out upside down. All the water in the vacuum will shoot up and into the filter. Doing this once should be enough to prime most filters if the canister already has water in it.
Regarding HOB filters, you can keep it, just put it on a timer so it runs at night. Then you get a lot of filtration at night when churn doesn't matter, and a calm surface during the day to keep in the co2. Just make sure that the filter side of the U tube is below water level so the U tube keeps water in it when it's off, otherwise it'll syphon out the filter and de-prime itself.