Your "Wet Reckless" conviction can be a bar to entry into Canada because it is a alcohol related driving offense. The Canadians equate driving under the influence on the same level as attempted murder and a DUI offense will be a bar.
However, as far as I understand the Canadian immigration system, (I am only licensed in the State of California and I have no knowledge of the Canadian system) an expungement under 1203.4 eliminates the offense for immigration purposes.
Remember that the Canadian Authorities have access to the same database that the FBI uses, the NCIC, and they will see your conviction on your record, if they chose to look it up.
It's hard to believe an immigration attorney wouldn't know the term "wet reckless." For Mr. Shusterman's benefit, "wet reckless" is legal slang for a DUI (Vehicle Code 23152) that is reduced to reckless driving (Vehicle Code 23103) pursuant to Vehicle Code 23103.5.
The punishment for a wet reckless includes a lower fine and a shorter DUI class than a DUI conviction, there is typically no jail time, and it does not result in a license suspension (although DMV may suspend your license under a separate procedure). It still counts as a prior DUI conviction for any new DUI prosecution within the next ten years. Your insurance company will probably treat it as a DUI, too.
I agree with Mr. Radtke that your 1203.4 dismissal may take care of your Canadian travel concerns, but I would contact the Canadian consulate to ask first. They can let you know whether you'll be admitted, or whether you'll get turned back at the border.
Also, note that the 1203.4 dismissal will NOT prevent your wet reckless conviction from being used as a prior DUI conviction in any future DUI case.