Yellowstone national park proposal spot

I would like a painting of the scene that I proposed in for my now fiancé to give as a wedding gift.

It’s a spot by a river in Yellowstone national park around an hour before sunset with forest and mountains in the background.

I have a series of photos and videos of the scene.

I’d like your advice on size - a1 or a2 feels right to me.

My wedding is in September so this would need to be completed and delivered by the end of august.