Yes, Virgin West Coast will also now allow you to select your seat if you book through them. You also get the option of booking an e-ticket (print it out) or m-ticket (you need to install their app) which is also compatible with Apple wallet and the like, if your journey is 100% with them (which Euston-Manc is).
If it's the weekend, you can also upgrade onboard for £20 each way. The downside of this vs upgrading beforehand is that you don't get lounge access.