Depends if your provider is willing to coperate. Bonding needs support on the provider side also.
Without that, you can do load balancing in many ways, but that will not give you 1+1=2 speeds. PCC and ECMP are some of the options in this case, you can see here for more: http://wiki.mikrotik.com/wiki/Manual:PCC
Are those different Internet providers? If it is just one, negotiate the solution with them directly. If they are 20 independent providers you would need your concentrator point hosted somewhere with gigabit duplex connectivity to join all those streams transparently together.
If you’re doing load balancing via different un-bonded links, then you can’t get a single transfer to go faster than whatever link it’s being routed across.
Think of adding more lanes to a highway - you can get more cars/time through the same road, but you still must obey the speed limit.
So if the various links are through different ISPs or through multiple unbonded circuits to the same ISP, then you could reach a total capacity that’s close to the sum of all links, but nobody could ever download at the total capacity (single thread download - peer2peer and multi-stream file transfer clients could use them all)