I am a Canadian citizen and my wife is a Hong Kong citizen and holding the Hong Kong (one of the visa-exempted countries) passport. She is now staying in Canada as a visitor. She has just submitted her Permanent Residence (PR) status application under the sponsoring spouse category two weeks ago and I am the sponsor of this application. We have plan to travel to US in January, 2018 however the guide to Sponsor your spouse, common law partner, conjugal partner or dependent child says that "If your spouse or common law partner leaves Canada while the application is being processed: there is no guarantee that they will be allowed to reenter Canada. This is especially true if they need a visitor visa." Having said that is there any workaround, alternative or exception for my wife to be able to reenter Canada following the trip to US in the coming January? Otherwise, she may have to cancel the trip. Thanks.
First of all, did you apply outland or inland? Your statements suggest inland, but never assume.
If you applied outland, then if she is denied entry as a visitor and has to go back to HK, her application still continues to be processed.
If you applied inland, then if she is denied entry as visitor, basically the application will run into a big problem because she ends up not being in Canada during the application which is a condition of inland application. This is the reason why people who applied inland stay in Canada for the duration, because leaving Canada does not guarantee re-entry again, no matter how small the possibility of being denied re-entry, it is still a possibility.
So inland means the PR applicant stays in Canada during the process, and is eligible to apply for open work permit (OWP). Outland application does not offer the option to apply for work permit, as by definition of outland, the person is not living in Canada. Living in, and being a visitor are 2 different things. As a visitor, you do not "live in" Canada.
In case you do not know, outland application does not mean that the applicant stays outside Canada. The person can also be in Canada as a visitor during this time, but have no other status, such as employment, and hence the difference between outland and inland.
Edit/addition: since writing this, I am not entirely sure if the OWP process/option is still valid, and therefore whether the inland/outland distinction still holds. The OWP program according to CIC website says the information is "archived", and the program was only extended until Dec 2016. Others with up-to-date knowledge of this can pitch in.