1.) The answer is in the region specific forms, check there. This is DIFFERENT for different regions, so make sure you have the right region specific guide.
2.) The medical should always be done BEFORE sending in the application and the form you get from the doctor sent with the application.
The police clearance should normally also be done BEFORE sending in the application and submitted with the application. I say normally because not all countries are willing to issue one until the visa office asks for them. Hong Kong is one example - look at the instruction on how to get the police certificate from Hong Kong here:
http://www.cic.gc.ca/english/information/security/police-cert/asia-pacific/hong-kong.aspYou can't get a police certficate from Hong Kong until the visa office sends you a letter requesting it and the visa office won't sent that letter until they've received your application, which is why if you need a police certificate from Hong Kong, you send it after the initial application.
So if your wife needs a police certificate from Hong Kong, you include a letter with the application stating you can't get it yet, but will be happy to provide it once the visa office requests it. It's the same in Singapore. I haven't checked all the others, but those seem to be the only two that work that way. If you CAN obtain the police certificate before sending the application, then that's what you should do.