We've had a mixed assemblage of 150+ redpolls in our yard for a few weeks. Most have been "Southern" Common Redpoll (Acanthis flammea flammea) with a smattering of "Greater" Common Redpoll (Acanthis flammea rostrata).
A couple of "Southern" Hoary Redpoll (Acanthis hornemanni exilipes) were joined today by a "Hornemann's" Hoary Redpoll (Acanthis hornemanni hornemanni). These photos give a sense of the larger size of Hornemann's Hoary Redpoll relative to the Common Redpoll in the foreground.
Over the previous two winters I've spent some time observing Ontario's four recognizable redpoll forms - you'll find notes, tons of photos and related links here.