In this case measures means "rules" or "standards"
For example as in air pollution, it is planned to agree to a 10% reduction this year and 20% reduction in 3 years. Those new numbers or goals are the "measures". It can also mean the steps toward reaching a goal.
Their actions were motivated in large measure by a desire for revenge.
She felt equal measures of hope and fear.
In the 2 sentences above it means "amount"
The TSA has implemented new airport security measures (here it means procedures)
Adopted (in your example) means "agreed to".
TO restate the sentence you provided:
The goals (or procedures) that the US and Canada have agreed to are a good start [toward reducing air pollution in North America.]