、！
Groaning about something, he's throwing his bursting passion onto the canvas!
Literal
Something groan-[while-ながら], gushing passion [obj-を] canvas [on-に] is-slamming!
Dramatic description of an artist at work. なにやら ('something, somehow') is a literary indefinite adverb. 唸る ('to groan, to moan, to growl') describes the artist's intense vocalizations. ほとばしる ('to gush, to burst forth') is a vivid literary verb, often for liquids, light, or emotions. パッション is the loan 'passion.' ぶつける ('to hit, to slam, to throw at') is a verb of forceful contact. The sentence paints a vivid picture of an expressionist artist.