One of Boston’s biggest office tower landlords is partnering with a mainstay of the Seaport District’s marine industrial park on long-term real estate opportunities.

Toronto-based Oxford Properties formed a joint venture with Pappas Enterprises for the $25 million purchase of 370 West First St., which contains a Yankee Lines bus garage, and 655 Summer St., a 1.4-acre property containing a small office building, which sold for $10 million.

The partnership will continue marketing and leasing the properties, while exploring long-term strategic planning and investment opportunities, the two companies said.

“By partnering with Oxford Properties, we can consider the most impactful ways to maintain a vibrant tenant mix across these two assets,” Timothy Pappas, CEO of Pappas Enterprises, said in a statement.

Oxford is the real estate arm of the Ontario municipal employees pension fund and has acquired eight class A office buildings in Boston and Cambridge since 2014. It’s also proposing a 24-story office tower at 125 Lincoln St. in Boston’s Leather District, replacing a parking garage and office building.

There are no immediate plans for new development on the two Seaport District properties, the companies said. The Summer Street location is across the street from the 411-room Marine Wharf hotel current under construction at 660 Summer St.

“The location and future potential are outstanding and we are looking forward to being long-term partners with Pappas Enterprises,” Chad Remis, head of Oxford Properties’ Boston office, said in a statement.