I'm a little confused by the power standards. as far as I can tell, USB PD (power delivery) specifies a maximum of 2.1A.
The RPI3 requires recommends 2.5A, 0.4 more than the spec. Canakit's power supply is 3A.
I'm thinking that a 3A USB-C (different spec) would work with the appropriate USB-C to micro USB adapter. There's a google engineer who tests USB and says to stay away from these cables because they violate the USB spec, but it seems like Canakit is selling something that violates the spec too.