Upload & Sell: On
The premise is limited and the choice obvious.
If you have no limit on the budget but can get only one body, you obviously get the flagship Canon DSLR, the 1D X.
If you have no limit on budget but can get only one lens, then obviously get the widest range of focal lengths. That would be the 28-300 mm L. Even though it is on the slow side (small aperture) that is compensated for by the high ISO capability of the 1D X. There are sharper lenses but get capability before refinement.
I like your idea, I will pass on your suggestion to him, 1Dx with 28-300L. Thanks