We use MUST when we say something that is essential or necessary. e.g. You must visit us soon. Must is a modal auxiliary verb. It is followed by a main verb. The structure is subject + must + main verb MUST expresses personal obligation. It expresses what the speaker thinks is necessary. Must is subjective. e.g. I must go home. HAVE TO is when we say that something is obligatory, e.g. children have to go to school. Have to is often grouped with modal auxiliary verbs for convenience, but in fact it is not a modal verb. It is not even an auxiliary verb. In the structure, "have" is a main verb. The structure is subject + auxiliary verb + have + infinitive (with to) e.g. I have to go to work. Have to expresses impersonal obligation. The subject of have to is obliged or forced to act by a separate, external power (for example, the Law or school rules). Have to is objective.

Technically the are the same. However we usually refer 'can' as a can drink/food in liquid form e.g. a can of coke, a can of vegetables soup whereas 'tin' refer to solid food such as a tin of sardine, a tin of pineapple chunk and a tin of Danish cookies.