The GVA-IAD flight is operated by UA. If you buy a separate ticket, also operated by UA, for IAD-YOW, I am confident that UA will tag your bags through - in which case you can connect midfield in IAD (you will have to pick up and re-drop your bag within the transit facility).

I have transited IAD midfield arriving from that GVA flight several times this year and immigration was always very quiet - the GVA flight is one of the first to arrive. Perhaps I got lucky but even with bags, it never took me more than 30min including security. I have Global Entry but the time saved there was just spent waiting at the baggage belt. By the time my bags came out, pax coming through regular immigration were beside me.