The Toronto Stock Exchange posted its April block trading statistics this morning, and the numbers raise an interesting question about who is in, and out, of the planned Alpha trading system. The TSX statistics show GMP Securities was the top trader on the Canadian exchange, with 14-per-cent of the buying and selling as measured by volume. TD Securities edged out BMO Nesbitt Burns as the biggest trader by value, with each enjoying 13-per-cent market share. Canaccord Capital ranks 10th by volume. These standings are consistent with what's been seen over the past year. The question, then, is why Canaccord was invited into seven-dealer group that founded Alpha, along with the six bank-owned dealers, while GMP Securities was left out. Alpha is an alternative stock trading system that's meant to challenge the TSX when launched in 2008. To date, each of the founders has thrown in $1-million to get the system rolling, with everyone committed to at least $10-million more. The simple reason that Canaccord is in the club lies in type of business this dealer does. Canaccord counts an enormous number of individual investors in its customer base. Many are active traders in junior stocks. These are ideal clients for a fledgling exchange, as they generate a great many small orders that are best matched by computers, rather than human traders. This electronic buying and selling is known as passive order flow. GMP, on the other hand, has an institutional focus. Most of its stock traffic involves human beings moving blocks of shares between money managers, and then reporting the trades on an exchange. This is called active order flow. While block trading underpins a great franchise at GMP, it's not as important to the success of Alpha's network, which requires lots of little orders to build liquidity. If Alpha gets up and running - there are a great many of us who believe this is all a big bluff to force lower fees out of the TSX- GMP will certainly be invited to join. But as Alpha takes shape, trades from the ordinary retail investors who patronize Canaccord are of paramount importance.