From a scholarly standpoint the essential difference between Hinayana (the small or little vehicle), which carries with it a derogatory connotation, and Mahayana (the great vehicle), more than likely boils down to a matter of a closed canon (Hinayana) versus one that is open (Mahayana).
However, one thing is for sure, Buddhist scholars can easily differentiate between discourses revered by Hinayanists and those revered by Mahayanists. Still, this is not to say Mahayanist do not revere the discourses revered by Hinayanists such as those making up the familiar Pali canon and the Chinese Agamas.
When the Chinese Buddhist monk, I-ching (635–713), of the T’ang Dynasty traveled to India he reported of the Buddhists he saw that, "Those who worship Bodhisattvas and read Mahayana Sutras are called Mahayanists, while those who do not do this are called Hinayanists."
This is a statement not lacking in some measure of truth for in the past Hinayana and Mahayana monks lived together. Each it appears to have been tolerant of the other. In other words, there were very little external differences between the two. Again, the difference seems to boil down to the canons accepted by each.
Having studied both the canon revered by Hinayanists (the Pali canon) and a number of Sutras revered by Mahayanists, it is not difficult for me to find so-called Mahayana thought throughout the Pali canon and even in the commentaries I have read. Arguably , both canons revolve around mind's liberation and both point to the transcendent. I would also have to argue that both deploy the via negativa as a means for reaching the absolute and meditation (jhana/dhyana). I will go even further and say Mahayanists embrace both canons whereas Hinayanists tend to stick with the Pali canon.
If one actually goes looking for the similarity between both canons, they can find a great deal in common between them. If there are differences between the two canons, the differences are mainly either external or sectarian in which members of a particular school hold the view that the Buddha categorically denied the self while, at the same time, admitting a hybrid self based on the Five Aggregates. On this note, this doctrinal position has been attacked a number of times even by members of the Theravada sect that market anattavada (i.e., there is no self). For example, the Theravada monk Buddhadatta argued that the Buddha was never an anattavadin who denied the self (cp. The Buddhist, XVI, 9 1946). Another example, the huge Dhammakaya Foundation of Thailand which is Theravada in no way endorses anattavada. They even claim nirvana is the same as the true self which can only be verified through profound meditation.
Nothing is really to be gained by looking through the Pali and Mahayana canon for cardinal differences. Both, I can say, help the other. Looking at my small library to the right of me I use the Pali canon more than I use the Mahayana. But when I need to get a more expanded explanation of Mind or Self, I go to the Lankavatara and Mahaparinirvana Sutra. But I never think, this is Hinayana; this is Mahayana.