Interesting question. However, Mongo thinks you might be hard pressed to have anyone who has even tried the 200-400 Canon - let alone owned one to be able to answer your question.

from Mongo's experience, he has had the 200-400 f4 Nikon for a few years. Not the same lens in many respects. However, Mongo can say that if he had his time all over again, he would have bought the 400 f2.8 instead. Main reason being that he uses the lens at 400 mm 98% of the time and has a x 1.4 converter the rest of the time. The 200mm up to 400mm range almost never gets a look in.

if Mongo were you, for your purpose, he would also take along that second camera body he has with the 70-200 f 2.8 ( with or without a X 1.4 converter) or just the lens combo without the second body and take your chances swapping lenses. Not ideal but it is an option.