Resources for Cantonese speakers learning Mandarin?
Pleco is selling two unique dictionaries that could help you:


  Guangzhouhua Fangyan Cidian
  
  $9.99 (version 3 only)
  Chinese-Chinese dictionary of Cantonese-specific vocabulary with approximately 8000 entries, from Commercial Press. 


and 


  Guangzhouhua-Putonghua Cidian
  
  $9.99 (version 3 only)
  Cantonese-to-Mandarin (focused on diffs between them), 10k entries


A problem you might find in Cantonese is that, while there is a measure of standardization, overall standardization is lacking.

Take 剩翻 for instance.

If you search it by character in Pleco you will only get one result:

剩翻


  剩翻 zing6 faan1 {shèng fān}
  
  this is what's left


That might work for you if you're looking for English results and even if so maybe not because of the poor quality of the English.

But if we use Jyutping:



we can see all the results with the sound we're looking for and may even find out that 剩翻 is written 剩番 in most dictionaries.

Pleco also has a number of Cantonese to English or English to Cantonese based products as well.


  ABC Cantonese Dictionary
  $29.99 (version 3 only)
  Brand new (published in 2017) Cantonese-to-English dictionary, the first new one in several decades; featuring 16,000 Cantonese-specific vocabulary entries and a whopping 15,000 Cantonese example sentences (all with Jyutping/Yale pronunciation). Edited by Robert S. Bauer and produced by Wenlin Institute. 





  The Right Word in Cantonese
  $9.99 (version 3 only)
  English-to-Cantonese dictionary focused on idiomatic translations; 6500 entries 





  CC-Canto Cantonese-English Dictionary
  Free
  Pleco's first self-published dictionary project, an open-source Cantonese-to-English dictionary with about 25,000 entries, designed as a Cantonese extension to the open-source Mandarin dictionary CC-CEDICT that's built into Pleco. (basically, we only define words when they don't, or when their definition differs from the Cantonese one). 
  
  Also available online at our website cantonese.org - much more information on the project is available at http://cantonese.org/about.html