In fact it depends on the loadbalancing method you use for the etherchannel. You can use : src-mac | dst-mac | src-dst-mac | src-ip | dst-ip | src-dst-ip | src-port | dst-port | src-dst-port
If you're using mac based loadbalancing for an etherchannel between two router, you won't get any loadbalancing as the mac involved are always the same therefore the troughput will be 1G. These method are best used on uplink between Access and distribution switches. (src-mac on access side, dst-mac on distribution side or src-dst-mac on both side)
If you're using ip based loadbalancing, a pair of devices will always uses the same link (so 1G) but if there are a lot of flows you will have a better distribution and it wil behave like if you had +/- 2G. The key point here is that from machine A to machine B you will never get more than 1G even if they are the only users of the etherchannel. These mothod are best used on etherchannel between distribution switches or distribution to core switches where you have always the same mac but lots of differents src-dst IP pairs.
If you're using port based you will get max 1G per flow, therefore if you have two flows between machine A and machine B, you could (if you're lucky) have 2G if they are the only users of the etherchannel. These method are useable everywhere but are not available on all the platform (as far as I know).