Tilray shares were climbing 3% to $18.89, while Aphria was off slightly to $15.38 in premarket trading.
The combined company had a market cap of about $8.2 billion based on Friday's closing stock prices.
Tilray said its shares will continue to trade on Nasdaq under the ticker symbol "TLRY" after its merger with the fellow Canadian company, and will start to trade on the Toronto Stock Exchange under the same ticker from Wednesday.
Aphria shareholders voted to approve the merger last month.
The company said it expects to deliver about $81 million of annual pretax synergies within 18 months.
Aphria CEO and Chairman Irwin Simon said in a statement that "COVID-19 related lockdowns have presented unique challenges across Canadian and German markets."
"As these markets begin to reopen," he said, "Tilray is poised to strike and transform the industry with our highly scalable operational footprint, a curated portfolio of diverse medical and adult-use cannabis brands and products, a multi-continent distribution network, and a robust capital structure to fund our global expansion strategy and deliver sustained profitability and long-term value for our stakeholders."
Simon will lead the new Tilray, with Tilray's current CEO, Brendan Kennedy, joining the board.
In that same month Tilray also announced that it had reached an agreement with U.K. peer Grow Pharma agreed to import and distribute medical-cannabis products in the U.K.
Last month, Tilray reported a fiscal third-quarter loss that was much wider than analysts' expectations.