Okay guys, I need some help. I need to make a cake similar to this but I'm at a loss as to how to attach the smaller "paint can" to the board. I will obviously have to ice and cover it with fondant before placing it on the board and I know I can probably attach and ice the large cake like normal but how do you place another cake that will already be own its own board. Tape? Hot glue? will icing hold? Please help!!!! Thanks :)

I would use some buttercream to attach it to the board just like you would do with the large cake and then some more buttercream between the large cake and the "paint can" cake.  Looks like they are touching.

I use Royal or Chocolate because that's what I typically have on hand. BC is fine too. 

Each cake I make is always on it's own board that's the same size/bit smaller than the actual cake so I can pull it in/out of the fridge if needed. As long as they have their own boards you can put some glue between although I don't think it's necessary personally-if you do make sure you tell your client so they don't end up with a shirt full of cake trying to separate it. 

Hahaha, I laughed at the idea of this happening way more than I should have.

I agree with all the other replies EVERY cake you do should be decorated on it's own board that is the same size as your cake, so much easier and cleaner.

You can just pop a little of your icing on the fondant where you will be putting your cake on the board and pop it on - easy done. Even a few drops of water on to your fondant to make it tacky will make your board stick to the fondant.

I would use 2 sided carpet tape to secure the 2nd cakeboard to the board.  In humidity, I have had the royal icing melt and cake slid off the board...what a disaster!  Be safe rather than sorry!

I have done many similar arrangements.  Since I did most of my decorating in b/cream I just would plop a fair sized dab of that where each cake was to be set.  It holds it just fine.   I have lived in a dry, summer HOT area and never heard of/had any problems with the cakes moving.   I usually would have the cake finished at least a few hours before pick up - often the night before - don't know if that helped any.   If the cake was especially heavy I would use dbl sided tape. 

I always use hot glue under my cake circles. I don't trust frosting or icing of any kind to hold the cake to the board.

I learned that lesson the hard way!  Lol!