A petition and application may be filed concurrently when there is a visa number immediately available at the time of filing. Concurrent filing is always allowed for all immediate relatives of a United States citizen, since there are no numeric limitations in this category. However, in some categories, even if there is a visa number available at the time of filing, concurrent filing is not allowed as the intending immigrant must have an approved basis of eligibility (i.e. an approved petition) before being allowed to file for adjustment of status. For more information on if you can file concurrently, refer to the instructions on your immigrant petition:
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Generally speaking after filing the I-130/I-485 package your wife will not be able to return to Canada once the paperwork has been filed. If she leaves the country she is deemed to have abandoned her application and the case will be denied. So if she has to return to Canada in August your best bet is to hold off on filing the paperwork. I would also urge you to consult with an attorney about the I-94 issue.
If she leave the U.S. without a valid advanced parole, USCIS will consider that she abandon her AOS application.
This answer is of a general nature and should not be relied upon as final, nor is it intended as legal advice. Consult with a qualified attorney before making any legal decisions. Gen Kimura, (832) 247-6932.