Good evening, I would be happy to assist you.
A patent protects a unique or original design or idea and while food items and recipes can be protected by patents, they often won't qualify unless they are truly "unique". A Trademark protects a name or symbol, such as the Nike swoosh or the brand name.
Because it is often difficult to patent a food item or recipe, this is why you'll often hear things like the "cadbury secret" or "the colonel's secret recipe".
If a chocolate bar were produced with a unique design, say for instance the triangular Toblerone bar, the company can patent shape, but again, there must be a level of uniqueness involved and this can be tricky to demonstrate. For instance, look at M&Ms and Smarties. Both are very similar. They are both small, round, coloured, candy-coated pieces of chocolate. Candy coated chocolate isn't unique enough to protect with a patent and as a result, you have similarities.
So as for the recipe, unless you were using ingredients that were unique or rare or made with a special process, you likely won't be able to protect it with a patent. It would simply be a matter of keeping your recipe secret. However since you are talking about using Cadbury's chocolate, it would seem this doesn't apply to you.
You really need to look at your chocolate bar and determine what it is that sets it apart from others as this is what would be looked at for its uniqueness and what you'd be looking to protect. If it's the shape that sets it apart, then the molds used may be patentable. If it's the logo imprinted on the bar, then this would be a trademark issue, as you'd be looking to protect the name and logo on the brand.
As for manufacturing it yourself, there would be nothing improper about using Cadbury's chocolate. Cadbury sells its chocolate in various bar and candy forms and also sells it for baking in other products and as well, sells it in bulk for other purposes. There is no reason that you could not use Cadbury chocolate in your own bar, as long as you are making it distinct from any other Cadbury product in design and name and not holding it out to be a Cadbury product, coming directly from them as this would be misleading.
From the sounds of it, your idea would incorporate an existing recipe for chocolate (ie Cadbury), in a brand new design. If your design or production method is unique enough, or you have an idea for a name or branding that is your own, then you'll want to protect this.
Patents and Trademark registering can be costly, as you clearly recognize. However, it is possible for you to undertake this yourself and register it with the Canadian government to give you some protection and thereby, bargaining power. If you do it yourself, then you're just paying the filing fees to the government and not the large fees charged by patent and trademark lawyers.
You can find more information on the patent and trademark registering process on the following government of Canada site.
Please let me know if you require any clarification or have further questions as I would be happy to chat further.