Zinsser CoverStain Oil. It gives you the best chance for good adhesion. Stinks to high heaven so ventilate properly. If you don't like the idea of using an oil, there are lots and lots of quality latex bonding primers such as Zinsser's 123, Glidden's Gripper, Stix, etc. as well as the latex bonding primers from the nat'l paint chains if Canada has Sherwin-WIlliams, Benjamin Moore, etc.

 

I also use an oil base primer to make the switch. I'm old school and don't trust any of the latex primers ..... and I know oil primer will do the job. If you know the existing paint isn't lead based it's a good idea to scuff sand first. Wiping the existing enamel with a liquid deglosser is also a good idea.

 

Oil based primer is always going to be my first choice for this. Zinsser is the brand of primer I buy so I have no qualms about Gymschu's choice.

 

Scuff sand then BM 217, 024, primelock or Stix if you dont want to do oil.

 

There are paints that will stick straight to oil. BM cabinet coat, PPG Breakthrough, and Kelly Moore Durapoxy. Durapoxy would be my least trusted paint on oil though. Cabinet coat and breakthrough will stick like superglue.