Can I cast a glow in the dark flower in resin?
A few comments about the problem as a whole, before I address your specific question...

You are attempting to encapsulate something in a clear resin shell.  That shell lacks any distinct shape, being comprised of flat planes and soft organic curves.  It does not contain any sharply detailed features or surface textures.  In short, the shell probably does not contain any aspects which need to be captured by an advanced casting medium like silicone.

Consider Casting a mold using a mixture of Gelatin/Glycerin.  This avoids much of the cost of casting silicone.  Silicone is better in my experience for capturing details, but for your project, gelatin will probably work fine.

On a different subject, clear resins are notorious for capturing air bubbles which may detract from the look that you are pursuing.  There are techniques for reducing those bubbles but the only way to completely eliminate them is to use a vacuum chamber.  Here are some instructions on creating a cheap vacuum chamber.

Now for your actual question...

The containers which you show are suitable for holding your mold.  I prefer the red Wall's container because it seems to widen near the top.  That will make removing the mold from the container easier and leave the container intact between castings.  That way, once you have cut your original out of the mold, you can return the empty mold to the container to support its original shape during the application and curing of the resin.