Looks like Canada is giving this a shot as well. But here, they clearly say they may open the bag. Then you are pretty much screwed if you have a connecting flight in the US as the bag will have been 'tampered with'.

From the CATSA wbaite:
As of January 31, 2014, the Canadian Air Transport Security Authority will accept, subject to screening, duty-free liquids, aerosols and gels purchased from any airline or airport retailer that are properly sealed in official security bags and accompanied by a receipt.

These do not count as part of your carry-on allowance.

Screening officers may open your security bag to screen its contents, then re-seal it after inspection.

You may be asked to surrender your duty-free purchases if:

either the bag or the product within does not pass required security screening;
the retailer did not use an official security bag;
the clerk improperly packaged your purchases at the point of sale or did not include the receipt;
you opened the bag yourself after making the purchase and before screening; or
more than 48 hours have passed since you made the purchase (official security bags are only valid for two calendar days).
Please note that duty-free liquids, aerosols and gels may be intercepted if you pass through pre-board screening at a connecting airport in another country.

- See more at: http://www.catsa.gc.ca/duty-free-pur....FhbBoASs.dpuf