Yes I do believe dogs are sentient. They are concious and aware of their surroundings and self.
Kraidy, thats a good point. ME is set in a universe that is not one evolved from the one we know (sort of), so yes the deffinition of sentient and Ai could very well be different from we klnow (or think or assume etc etc).....
Garuda, good points, and I agree, legion shows much more self awareness and conciousness than EDI ever does throughout the game imo.
Baladas, well thats not really a very good analogy if I'm being honest, but will try to answer you. Basically, No yo your first question, as you say, there are too many variables to take into account despite training, tactics and planning etc.
As for Tim being intelligent enough, do you know what the majority of people I have met and dealt with who have diploma's, degree's, batchelors (whatver) have been some of the most stupid people? Intelligence, wisodm and being clever are all very different (even though they blur against each other at times), TiM may be very clever, shrewd, tactical even, but intllegent I do not think so. Look at the top of pretty much every major coropration in the world, and tell me if the heads are intelligent, clever or wise? Its not such a simple question to answer lol. I am very intelligent, but I am academically not so bright, I know people who got top marks through school, college and university, yet are so damn dumb its unbelieveable.
I know I went off on a tangent there, but just because of where TiM is, doesnt mean he is very intelligent, if that made sense

As for Garrus, he could be the worlds best soldier, but he can't account for the percentage of something silly happening.