American English: Can you

Solution 1:

Many words that don't usually take stress in English have two forms. They have a normal form called the weak form where there is most often a reduced vowel, most often a schwa, /ə/. They also have strong forms which occur when they are stressed or when they appear on their own stranded from their complements (there is a popular misconception that strong forms are always stressed. This is not true).

The weak form of the word can is pronounced either /kən/ or more often /kn/ where it will have a syllabic consonant in the form of /n/.

When in sentence initial position we usually hear the weak form in casual speech, but the strong form is also possible. The sequences Can I help you and Can you talk are likely to be said like this:

• /kn aɪ 'help ju/
• /kn ju 'tɔ:k/

There is also a popular myth that yes/no questions are normally said with a rising nucleus. In actual fact, when we know that the sentence is a question, because it is shown by the grammar, then we do not need to use a rising tone. The normal intonation pattern for a question follows the patterns that we see for declarative sentences. In the Original Poster's examples we can see the fact that the sentences are questions because they use subject-auxiliary inversion (Can I and Can you not I can and You can). [However, because the nucleus is likely to be said with a high falling tone, the starting pitch of the words carrying the nucleus will be much higher than the preceding words.]

For this reason the intonation pattern for the first sentence is quite likely to be as follows:

There will be a low level prehead for Can I. The nucleus help will be said at a high pitch and will receive rhythmic stress. The pitch will fall immediately for the last syllable you which will occur in the tail of the sentence and which will be said at a low level pitch.

Simlarly for the sentence Can you talk, there is likely to be a low level prehead Can you and then the nucleus, the word talk, will be said with a high falling tone.

Of course, the context and the dispositions of the speakers will heavily affect what type of intonation pattern they are going to employ. There are literally dozens of different tunes that could be used. However, the important thing to know is that yes/no questions do not require rising nuclear tones!

Hope this is helpful!