Hello
I don't really understand Your question. Etherchannel is a way to "bundle" multiple links between two layer2-devices in order to gain more bandwidth.
It's a bit unclear. Do You mean to etherchannel between an access-point and the nearest switch? In that Case I cannot see how to do this since all AP:s i know of only have one single ethernet-interface.
But if You mean to etherchannel between the 3750 and the 3560 that shouldn't be any problem as long as they are directly connected and there are more than one ethernet-connection available between them.
Br
Jimmy