Best way to cook a two bird roast? I've bought this for Christmas. It's a boneless turkey and duck rolled together with stuffing. What's going to be the best way to cook this?

Seeing as it's boneless and therefore has no cavities, I'm wondering about sous vide, but it'll need to be long and hot enough to tenderise the leg meat without destroying the breast meat? That's going to be tricky to achieve.

Or do I go for the throw it in the oven at 160 Celcius for a couple of hours then up to 220 Celcius to brown it for 30 minutes at the end?
In my opinion, sous vide is the way to go here.  Throwing this in an oven is going to mean that you are likely going to overcook the outside, by the time the inside is at a safe temperature.  Because you have to cook these birds whole, there is really no way to differentiate between dark and white meat no matter what approach you take. I would sous vide at a temperature that is slightly lower (by a couple of degrees) than you like, then toss it in a very hot oven (or hot pan and baste) to crisp the skin.