Visitor extension during PR processing

[Tocanadawego]

I asked this already it the TRV section but didn't really get much response, so I figured maybe I'd be more lucky here.
My son (14 months old) is here in Canada with me and my husband (PRs) on a visitor status. He is from a visa-exempt country. We applied for his PR through family sponsorship on June 5 and already received an AOR. However, his visitor status is coming to an end on August 22 and we need to apply for an extension. I began collecting the paperwork, but I am stuck with deciding whether we should ask for a less than 6 months extension, or more than 6 months extension. My understanding is that if we go for an extension of over 6 months, he will have to do a medical exam (although that wasn't listed in his checklist when I started the online application). I know he will need to have a medical for PR too, but I don't want to be in a situation where I do it for the visitor extension and then it expires before the PR process is finalized.
Have any of you gone through something similar? What did you choose when applying for a visitor extension?

 

[Wakki]

Assuming your child does medical exam in August 2018......the medical exam result is valid for 1year until August 2019.

Dependent Child PR sponsorship application from within Canada currently takes 10months to complete......if all goes well, before April 2019 the PR processing will be likely completed.......and the PR visa will have expiration date August 2019.......you dependent child could do in-canada landing and as a visa-exempt visitor should have not much problem of re-entry for landing.

http://www.cic.gc.ca/english/information/times/

I may be wrong but you may consider applying for more than 6 months extension.......also don't see any problem having to re-do medical.