Spectra is what's called a master limited partnership and owns interests in pipeline and storage facilities.
It already owns around 83% of Spectra, and is offering about 1.11 of its shares for each Spectra unit.
That values Spectra shares at $40.00 each, or a 5.6% premium.
Enbridge says the deal addresses changes caused by the loss of a U.S. tax allowance that will affect certain interstate pipelines held within master limited partnerships.
"Significant weakening of the US Master Limited Partnership (MLP) capital markets has adversely affected the growth opportunities for MLPs, including (Spectra)," both firms said.
"If (Spectra) were to continue as a stand-alone entity in such an environment, it would be required to transition to a self-funding model using internally generated cash flow."
Enbridge's shares eased 0.7% in early deals.