Substantial to say the least. Adding Russia to the Lend-Lease Act shortly before pearl Harbor was really opening things up.
Least anyone forget, Americans were also volunteering themselves by 1941. This might blow some younger Americans away, but we had the Flying Tigers in China. An all-volunteer force defending the Chinese homeland; I can see some with blown minds (where is that emoji?!). Forgotten history that China wasn't what it is now back then. These volunteers are on top of those that went to England, Finland and, yes, Canada.
My sins have come to face me, I can feel it
That I have lived my life in vain
And now I know I'll reap the seeds I've sown