Here's a thread from the Rogers Community which confirms that these Samsung S7 phones purchased from/through Rogers are factory-unlocked. And that the phones are designed to carrier-lock themselves the first time a valid SIM card is activated. The catch is that Rogers sells you a Rogers Wireless SIM card along with the Samsung S7, which they expect you will impatiently and excitedly insert into your new S7 phone - which would of course immediately impose an exclusive carrier-lock to their network (Rogers Wireless, Fido, Chatr).
My understanding is that Public Mobile has never locked any devices, indeed Public Mobile doesn't even sell any devices. I could find no NCK, NSCK, SPCK, CPCK, or SIMCK codes in the registry databases which identify as "Public Mobile", although Public Mobile could always opt to carrier-lock new devices as an MVNO subset licensed by Telus (at least in theory, if not in practice).
(Note that PM is currently partnered with Toronto-based phone reseller Orchard and, according to Wikipedia, "previously offered a small range of feature phones and Android Smartphones" before being reorganized as a Telus value brand in Feb 2015. To my knowledge phones purchased through these channels always were and still are entirely unlocked, though I could be wrong.)
A Public Mobile SIM card is perfect for your new Samsung S7. The phone might self-lock onto Telus (Telus Mobility, Koodo Mobile, Public Mobile), though I doubt it. Note that it is often difficult and costly (far more than the promised $50, lol) to unlock Rogers-locked devices because they are notoriously reluctant to lose business and will obstruct the unlock process as much as they are legally permitted (constantly delaying as they attempt to resell or upsell you a Rogers subscription).
