Unfortunately, the baking process would subject the seeds to temperatures far too high for them to survive, so, no, you would not be able to germinate and grow poppies from seeds taken off bread.
It is easy to buy poppy seeds of many varieties though and they are easy to grow. Each poppy seed head produces hundreds of tiny seeds so you will be able to harvest these and plant more poppies in future.
As a matter of interest, the Opium Poppy species Papaver somniferum is, as its name suggests, the source of the illegal drug opium, as well as the drugs codeine, morphine and heroin. Growing the plants to attempt to extract these dangerous drugs is illegal in many places for obvious reasons but the seeds are not illegal because they contain hardly any of these alkaloids.
The seeds from the Opium Poppy are used in baking to sprinkle on cakes and bread.
Here is the Wikipedia link that will tell you all about the subject:
There are very many varieties of the Opium Poppy and they make a colourful display when grown. The dried seed heads are also used for decorative purposes.