Both programs are accredited by "The Canadian Engineering Accreditation Board (CEAB)", so when you graduate you will get a degree in engineering from both schools.
I am not sure about Carleton, but McMaster offers unique 5 year programs along with engineering. Those include engineering and management, engineering and society & engineering and international studies.
You will get the same education from either school. Most likely the courses at the undergraduate level are the same (strength of materials, soil mechanics, structural analysis, hydrology, geology, concrete design, etc.)
Unfortunately, its competitive to get into some 2nd year programs at McMaster, and civil is one of those competitive programs. You need a good gpa in first year to get into civil; by good i don't mean 80ss. Management is even more competitive to get into. I don't know about Carleton, but they might let you into 2nd year civil even if you just pass first year eng. Now, there's that free choice thing here at mac. Basically, you get to pick anything you want in 2nd year eng (excluding management, biomedical and maybe chem&bio), provided you don't fail any courses (you can drop courses, but if you fail anything you lose the free choice!).
To get the free choice you need a good average in grade 12, i think you need above 90%.
You should base your decision on things that matter the most to you. Maybe if you live in Ottawa, it is easier for you to commute to uni (no need for residence and all the extra expenses).
It is really up to you where you want to spend the next 4-5 years. One last thing, if you can, try and take some computer related courses in high school, like AutoCAD and programming (it will benefit you because you take both in first year eng
)