Year-to-date deal volume slipped 2.3 percent to $130.3 billion from $133.3 billion in the same period last year, according to data released by Thomson Reuters on Thursday.

Global M&A activity shot up 64 percent to a record high.

Factors weighing on market sentiment include fears of a trade war between the United States and other countries, as well as a lack of a resolution of the North American Free Trade Agreement (NAFTA).

"NAFTA is obviously first and foremost in terms of issues out there, but there's just general political uncertainty globally," said Grant Kernaghan, Citigroup's managing director of Canadian investment banking, adding that Citi's pipeline remained robust despite the uncertainty.

Second-quarter volumes jumped from the first quarter, helped by a number of outbound deals. Bankers expect more such moves in the rest of the year.

"The Canadian economy is strong, corporate confidence remains very high and interest rates are conducive for M&A," said Darin Deschamps, co-head of Wells Fargo Securities Canada. "We will continue to see a high level of outbound M&A activity from Canadian pension funds and corporations."

But "we could see muted inbound M&A activity because of the trade uncertainty," Deschamps added.

Highlights in the first half include plans from a Blackstone Group-led consortium to acquire about 55 percent of Thomson Reuters Corp's Financial and Risk business for $17 billion, as well as Enbridge's C$11.4 billion ($8.7 billion) deal to buy Spectra Energy Partners and Enbridge Energy Partners.

"Regulatory risk and uncertainty has become a stronger headwind that needs to be carefully considered in the formative stages of deal-making," said Emmanuel Pressman, chair of the corporate department at Osler, Hoskin & Harcourt LLP.

"NAFTA uncertainty, alone, has not been an obvious impediment to deal-making. However, it potentially affects value expectations and is a key contributor to broader geopolitical headwinds."

Separately, Canadian equity capital market activity slumped 37 percent to C$16.9 billion in the first half of 2018, the lowest level in five years.

(Reporting by John Tilak; Editing by Nick Zieminski)

By John Tilak