I'm travelling from canada to dublin, ireland. Flying air canada to heathrow airport, then british airways to dublin, just wondering if I'll have to do customs at heathrow or when I get to Dublin. Any ideas.
You will go through passport control on arrival at Heathrow, and again in Dublin.
Go to this page of Heathrow's website: http://www.heathrowairport.com/heathrow-airport-guide/flight-connections/connection-guides Put in your details, and you will get the transfer procedure and the (estimated) time it will take. Remember that security, customs (control of goods), and immigration (passport control) are three different things. You shouldn't have to go through customs until you get to Dublin. Customs in Europe is usually a matter of walking through the "Green Channel - Nothing to De-clare" line. Immigration and security are what can take time.