I can't imagine that airline pilots do this ferry flight like routine ops. A three engine takeoff is very special. Imagine they lose another one, due to some bird strike or similar. I'd say this is serious test pilot stuff. After they are enroute, three engine flight is okay and no big drama.
Looks like they have done so much work on the wing that it will probably be a four powered engine flight ?
... Also why a that big freighter for just an engine?....
Maybe they want to bring the engine in one piece to Canada, i think the engine is to big for other freighter when it is in one piece. The other reason for the AN-124 couldbe that with this freighter it is possible to load and unload without any other equipment. You can drive in and out with a truck or something else.