In addition to cloud / visibility requirements, SERA only requires a pilot to be in sight of the surface to fly under VFR below 3000ft amsl…. Currently the MilAIP hasn't been updated to current criteria though.
You can fly under VFR above 8/8 cloud at greater heights, provided that you maintain the required minimum separation from cloud and flight visibility requirements appropriate to the airspace category and altitude / FL.
IFR is available whether flying in VMC or IMC; however, it is mandatory in IMC. VFR is only available in VMC.