From what we know of last gen, I'm guessing you could replace the Wii with the PS2, and the PS3 with the Cube, and you'll see similar graphs.
In lieu of a pretty graph, here are the numbers from financial statements of the half years. Two caveats:
1) The old numbers are for all of North America, but generally Canada numbers are proportionate to US, so just bump up all of the current numbers by 10%, and it's comparable.
2) I believe the old reported numbers are shipments, not necessarily sell-through, so if anything they're higher than actual sales.
November 2006 -> March 2007
PS3: 238k/month (launch period)
360: 466k/month
Wii: 422k/month (launch period)
April 2007 -> June 2007
PS3: 87k/month
360: 176k/month
Wii: 360k/month
March 2002 (covering October 2001-> March 2002)
PS2: 2.35 million -> 391k/month
XB: 2.24 million -> 448k/month (launch period)
GC: 2.22 million -> 444k/month (launch period)
September 2002 (covering April 2002 -> September 2002)
PS2: 7.35 million -> 1.2 million/month (this seems horribly wrong, but I guess when you sell a hundred million consoles, it happens)
XB: 1.91 million -> 318k/month
GC: 1.00 million -> 166k/month