The only problem I have found with the TSX large cross block trade missed your fill, some broker will give the fill to an in house client first I have benefited from that (should be first come first serve) and if you are making frequently changes to your bid price, the time it takes to register 1 to 2 min your order can lose priority (the market maker hates that),

'could be my broker or the TSX itself'

your broker will take your trades, place it with trader on the floor or most likely an electronic trader who use the exchange to execute the trade, the only issue you can have with the exchange is platform or software failure