The firm's Investor Sentiment Index stood at 24 points at the end of June.
That's down two points from the end of December and down five points from a year ago, when the index stood at 29.
Manulife says it found less enthusiasm for almost all types of investments, including fixed-income securities, investment properties, balanced funds and cash.
It says the main exception was a growing appetite for investing in the stock market.
The insurance and investment company says Canadians are cautious because of persistent global challenges to the economy without significant signs of recovery.