Can i merge two sources of bandwidth into one router ?

Yes, but that router must have 2 WAN ports, and its going to cost a pretty penny! I would suggest in looking into building a Linux router that will support 2+ WAN connections, then you will need to decide if what protocols go through what connection/ or you could set it up for fail over... Depends on what you are looking to do...

Couple links that will help you out.
http://www.netlife.co.za/archived-articles/12-linux-mul...
http://blog.dual-wan.com/2007/09/which-is-better-multi-...
http://www.newegg.com/Product/Product.aspx?Item=N82E168...