Preflop: Calling can be good here depending on how badly your opponents are playing and how the table is playing in general. Generally I would call here if the table is loose/passive preflop. If SB has been playing reasonably (I assume he is as you posted no read) his range here is probably low-mid pairs, Big aces, and suited connectors.

Flop: Pretty obvious raise when the action first gets to you (hand is strong relative to opponents ranges, but is still very vulnerable). You picked a good amount, prices opponents out but still isnt too much to be called
Now the SB checkraises. This can mean couple things: 1)Big pair/two pair/set- SB feels his hand is strong, but vulnerable if you are bluffing with the Ad. I think you will see a hand like this often in this situation.The opponent feared getting no action from worse hands if he bet out, so he decided to checkraise initially to get value and protect his hand.
2) Flush (non Ace high) - A flush would checkraise for the same reasons two pair/set/big pair would (protect hand/still get value). A flush seems somewhat likely here as there are various suited connectors that may have called preflop and flopped the flush. Also, even though its not that likely, the villain may have a flush lower than yours (34s).

Conclusion:Based on the villains most likely holdings, you must call in this situation. You are getting over 3-1 when you are beating a good percentage of his hand range. Also, you very likely have two outs when you are behind.