As many as four additional financial services firms may join the domestic bid to take over Canada's TMX Group, operators of the Toronto and Montreal Exchanges.

The Wall Street Journal reported that at least three and possibly four firms may join the Maple Group Acquisition Corp., which last month launched an unsolicited and rival bid for TMX in competition with the London Stock Exchange Group.

Maple said its $3.6 billion bid was worth 24 percent more than the LSE-TMX "merger of equals,'' announced in February. But TMX's board rejected the alternate bid.

Desjardins Financial Group, GMP Capital and Dundee Capital Markets are among the firms in negotiations to join Maple, according to the Journal report. The consortium is also in talks with another large unidentified financial-services institution to join the effort.

The Maple group includes CIBC World Markets, National Bank Financial, Scotia Capital and TD Securities Inc., as well as Alberta Investment Management Corporation, Caisse de depot et placement du Quebec, Canada Pension Plan Investment Board, Fonds de solidarite des travailleurs du Quebec (F.T.Q.) and Ontario Teachers' Pension Plan Board.

TMX shareholders are set to vote on June 30 on whether to approve the proposed merger with the LSE Group.