Take your Office Depot ad to Staples and price match the Canon D420 for $129.99.
Then, use the $5/$25 Staples in-ad coupon.
Then submit for the $99 Staples Mail in Rebate here.
After reading everything, this deal should work NO PROBLEM, but make sure to save your receipts in case things get complicated.
We're going to try this one out, so cross your fingers!
(Thanks, Deal Seeking Mom!)