「大阪は食べ物がおいしいです」
or
「大阪に食べ物はおいしいでし」
are both sentences good ? What's the difference?

質問を翻訳

で = place where some activity takes place
に = place where something exists/is located

For this sentence neither で nor に is to be used because it doesn't say anything about an activity or the existence of something. You have to say either 大阪は食べ物がおいしいです or 大阪の食べ物はおいしいです