Canu assembly not making a single consensus?
Looking that the link you provided only 30% of the reads appear to be e. coli.  I would suggest filtering the reads for those that align to e. coli and see where that gets you.  Did the original publication describe the method they used for data cleaning? 

A: 

https://trace.ncbi.nlm.nih.gov/Traces/sra/sra.cgi?run=SRR3385327

Unidentified reads: 68.82%
Identified reads: 31.18%
cellular organisms: 30%
Bacteria: 30%
Proteobacteria: 28.09%
Gammaproteobacteria: 19.7%
Enterobacterales: 13.3%
Enterobacteriaceae: 12.54%
Vibrionales: 0.01%
Viruses: 1.17%


B: 

Without a good assembly canu won't be able to determine if the assembled genome is circular.  I would ignore this until you have a good example.