Incentive is key. I like both of the above ideas although I would adapt them both. You can't force people to see their doctors. It's very difficult even finding a family doctor where I live. How then to implement?
1) Make it a program to opt into, therefore only the healthy people that benefit from the incentive will opt-in. Thereby defeating the purpose.
2) Force all Canadians to get a physical within 3 months of doing their taxes. This will be labelled as draconian and fought tooth and nail by conservatives and liberals alike. Many people have a healthy fear/irrational phobia of hospitals/doctors as well. During the physical, the doctor will provide you with nutritional literature and sign a form stating your overall BMI/general health.
3) Tax the worst culprits, fast food and products with high HFCS. The corn lobby will freak the fuck out and conservatives will lament another "useless" tax. Fast food is big money. As is coffee. This won't go over well.
4) Subsidize farmers (dairy) into growing more fresh local non GMOproduce. Provide a framework for distribution for all Canadians, rural and urban. Don't waste money on ad campaigns and information because unhealthy people will ignore it anyways.
5) Incentivize food processors to use/reduce HFCS in their products. Look at coke stevia for example. Or mexican coke that still uses cane sugar and is super delicious.
6) Genetic testing in children to identify markers to predict at-risk individuals.
None of these alone is enough to effect lasting change on enough Canadians to make a difference but a combination of some/all of them could have a noticeable effect.